Fracturing involves sequential isolation of part of a borehole so that a perforating gun can initiate fractures followed by delivery of pressure to the fractures to open them up further before production begins. Typically a plug is at a lower end of a bottom hole assembly (BHA) and the perforating gun is above. The plug is set and the gun is released and fired. The plug can have a passage through it with a surrounding ball seat. Before the fracturing starts a ball is landed on the seat and pressure is built up to open the fractures made by the perforating gun.
One way to expedite this process is to have the housing for the ball as part of the BHA to cut down the time and some uncertainty of dropping a ball from the surface to the seat in the frack plug before the pressure pumping operations can take place. To also save time in these operations the BHA is run in on wireline and delivered to the desired location with the aid of pumped fluid for the reason that often the desired location is in a long horizontal run.
In typical plug and perforate systems the bottom hole assembly (BHA) comprises an isolation device with a passage through it and a surrounding seat on the passage for an object to land on the seat and obstruct the passage. The object can be delivered with the isolation device or pumped to the isolation device after the perforating guns are shot and removed from the borehole with the setting tool for the isolation device. Delivering the object with the isolation device has the advantage of saving time to get the passage in the isolation device closed as compared to pumping down an object from the surface. However, this prior method has a drawback if the guns misfire. In essence, if the guns misfire they must be removed and new guns run in to the desired location which is frequently in a horizontal portion of the wellbore. Thus, gravity is not much help in running in the replacement guns. Furthermore, if the object was run in with the isolation device, then the object would be forced against the seat in the passage of the isolation device if any effort to use pressure or flow to deliver the replacement guns was employed. The closing off of the passage in the isolation device means the replacement guns cannot be delivered on wireline with a pressure or flow assist and that alternative means such as coiled tubing or tractors have to be used to get the guns into position. This adds enormous expense to the operation and creates issues of delay. Even if the object is dropped after the misfired gun is removed, it still takes time to pump the object from the surface to the seat on the isolation device that is thousands of meters away costing time and additional fluid displacement.
In the past one way to cut the time to get an object seated on a seat in an isolation device was to include a ball release device above the guns. The idea in US 2013/0175053 was to release the object into the annulus from above the fired gun and have the object make its way around the fired gun and the isolation device setting tool to a seat on a passage in the isolation device. A physical pull on the wireline sheared an unnumbered pin and allowed a ball 24 to escape through a lateral opening 28 to make its way toward the isolation device 14. There are many issues with this design. Frequently the guns 18 have very low clearance around them to the casing 12, which means the ball 24 will not fit in the annular space or would have to be so small that the passage in the isolation device 14 would also have to be small. A smaller passage in the isolation device could mean delays if a replacement gun has to be delivered with flow after an original gun misfires, as well as reduced flow-through rates that would limit a wells ability to flow back and produce through the isolation device in the event of sanding out. The spent perforating gun could also have burrs and sharp edges that could hang up or damage the object so badly that it might not seal at all when landing in the seat. Finally, in a horizontal run the object may not actually land on the seat if the seat surrounding the passage in the isolation device is considerably smaller than the casing inside diameter, a condition made necessary by the object being small enough to travel past the gun in the surrounding annulus around the gun.
Generally related to operation of lateral passages that can be selectively opened in a fracking context are US2013/0024030 and US2013/0020065.
In an application entitled Pressure Actuated Frack Ball Releasing Tool filed in the US on Mar. 10, 2014, with a Ser. No. 14/202,974, the pressure wave generated by the firing of the gun was sensed and a ball release mechanism was triggered to release the ball onto the seat of the adjacent frack plug. This device required sensors for sensing the pressure wave and then actuation of an independent hydraulic circuit to actually launch the ball.
Another phenomenon that occurs when the gun is fired is that there is a sudden acceleration of the string followed by a deceleration in an oscillatory movement back and forth until another steady state is reached. The present invention capitalizes on this movement pattern to release a potential energy force that propels the object and in the case of a fracking operation allows the ball to reach the seat of the frack plug to plug off the passage through the plug so that pressure can be built up and the fractures initiated with the perforating gun can be further propagated.
U.S. Pat. No. 5,020,609 illustrates a compensation system to offset acceleration forces in an unrelated context that uses a mass in tandem with opposed springs.
The preferred embodiment of present invention capitalizes on the relative movement created during acceleration to release a lock on a potential energy source to launch an object to another tool in furtherance of the fracturing operation. Other applications are envisioned where a gun is fired that creates string acceleration or in other contexts where acceleration or deceleration creates relative movement that can be harnessed to operate a tool. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawing, while recognizing that the full scope of the invention is to be determined by the appended claims.